Down-hole hammers generally comprise a drill bit as the lowermost component in the hammer assembly. The drill bit has a major diameter portion referred to as the bit head, and determines the diameter of the hole drilled. The bit head is traditionally integral with an upper, splined bit shank, which is slidably engaged and retained within a driver chuck. The driver chuck has an internal spline for engagement with the drill bit shank spline, and an outer threaded portion to engage a down-hole hammer barrel.
The bit shank splined section, when engaged within the driver chuck, is mechanically engaged rotationally, but is free to slide axially. To limit the extent of axial travel, and to prevent the drill bit from sliding out of engagement altogether, the drill bit shank has a section of reduced diameter above the spline, for a distance equivalent to the desired travel length of the spline plus the thickness of a retaining mechanism. This retaining mechanism is a bit retainer ring, made of two semi-circular sections with inner and outer diameters that are placed from each side around the reduced diameter of the bit shank thereby forming a near complete ring. The final section above the reduced diameter is the bearing land, which varies in form but is always of substantially larger diameter than the reduced diameter, so as to limit the axial travel as the bearing land comes to rest on the bit retainer ring.
In use, the driver chuck is lowered onto the drill bit shank, with the mating splines engaged. The two halves of the bit retainer ring are fit to the reduced diameter portion of the bit shank and rest atop the driver chuck. The drill bit, chuck and retainer ring sub assembly are threaded into the down-hole hammer casing/barrel. The bit retainer ring, now encased circumferentially within the down-hole hammer barrel, driver chuck below, and drill bit guide bush above, permits limited axial travel of the splined engagement.
It would be desirable to reduce the manufacturing cost of drill bits. The most effective way of doing so is to redesign the product so as to reduce its mass and length, while maintaining a robust and practical product.
EP1757769A1 discloses splines machined into the casing, a chuck fitted from above and a drill bit screwed into the chuck from below, providing for a shorter and more cost effective drill bit.
WO2008044458A2 discloses a type of drill bit for down-hole hammer use that is designed to be short and efficient to manufacture and use.
WO2009124051A2 discloses two embodiments of drill bits for down-hole hammer use that are designed to be short and efficient to manufacture and use.
WO2007077547A1 discloses a drill bit with a shorter shank than conventional types, also having threaded attachment.
My prior application, identified in the first paragraph above, disclosed embodiments of the invention illustrated in FIGS. 1-6 of the drawings. The description and claims below describe new embodiments, illustrated in FIGS. 7-9.